It is difficult, using standard electrophotographic techniques, to make any useful number of copies of an original document. Either the entire process must be repeated for the required number of times, or else an electrophotographic lithographic master must be made which can print the multiple copies. The former process is time consuming and expensive since the entire process must be repeated for each copy. The latter is economical only for relatively large numbers of copies since the master cannot be reused and an offset printing press is required in addition to the electrophotographic apparatus.
There are techniques in the literature which offer hope of improved performance, which have not as yet been brought to acceptable levels of commercial acceptance.
A process which can tone and transfer the toned image to plain paper and then retone and retransfer the image, without the need to reimage, has economic advantage. Because the latent image bearing insulator would not have to be resensitized and reimaged, the commercial process of making multiple copies would be greatly simplified and economies realized. In addition, the need for a master would be eliminated.
Previous techniques for accomplishing this have been severely limited in the number of usable copies which could be made, since the electrostatic latent image is inevitably degraded in the retoning and retransfering steps. Either there is uniform corona breakdown between the paper and latent image during the transfer step or the developer mix is sufficiently conductive to discharge the latent image during the toning step. Both of these problems inherently limit the number of copies which can be made with reimaging the photoconductor or image bearing dielectric.